JPH03257858A - Thin film capacitor - Google Patents

Abstract

PURPOSE:To form a thin film capacitor having a high-insulating characteristic and high-dielectric constant by using a film of specific elements and silicides or oxide thereof, which generate no surface roughness in a high temperature process, for the lower part electrode of a thin film capacitor. CONSTITUTION:In a thin film capacitor being formed on a board 1 having the structure, where a lower part electrode 3, a dielectric 4 and an upper part electrode 5 are by turns laminated, when the thin film capacitor is formed, where the lower part electrode 3 directly filming the dielectric 4 consists of one or more materials selected from rhenium, rhenium oxide and rhenium silicide, or where the lower electrode 3 consist of one or more materials selected from osmium, osmium oxide and osmium silicide, or where the lower electrode 3 consists of one or more materials selected from rhodium, rhodium oxide and rhodium silicide, or where the lower electrode 3 consists of one or more materials selected from iridium, iridium oxide and iridium silicide, dielectric breakdown strength is three times larger than the case where a conventional Pd film is used thus enabling excellent insulation to be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a thin film capacitor used in small electronic circuits (prior art) With the development of integrated circuit technology, electronic circuits are becoming more and more compact, and various electronic circuits The miniaturization of capacitors, which are essential circuit elements, is also becoming increasingly important. Thin film capacitors using dielectric thin films are used by being formed on the same substrate as active elements such as transistors, but while the miniaturization of active elements is progressing rapidly, the miniaturization of thin film capacitors has lagged behind. , has become a major factor preventing even higher integration. This is because conventionally used dielectric thin film materials are limited to materials with a dielectric constant of 10 or less, such as 5i02, Si3N4, etc. There is a need to develop large dielectric thin films. BaTiO3, which is a perovskite oxide represented by the chemical formula ABO3,
Oxides belonging to ferroelectrics, such as 5rTi03, PbZrO3, and ilmenite-type oxides LiNbO3 or Bi4Ti3O12, have a dielectric constant of 100 or more and as much as 1oooo in single crystal or ceramic in the above-mentioned single composition and mutual solid solution composition. is known and widely used in ceramic capacitors. Making these materials thinner is extremely effective in reducing the size of the thin film capacitors mentioned above, and research has been conducted since before the advent of technology.

Among them, an example with relatively good characteristics is the paper published in Proceedings of the IEEE, Vol. 59, No. 10, pp. 1440-1447. Yes, Ba film formed by sputtering and heat treated
16 (made at room temperature) to 1900 (12
The dielectric constant was obtained (heat treated at 00°C).

(Problems to be Solved by the Invention) The conventionally produced dielectric thin films such as BaTiO3 as described above require high temperatures during the production of the thin film in order to obtain a high dielectric constant. It was created on a lower electrode made of a melting point noble metal material.

Aluminum, nichrome, copper, and the like commonly used as electrode materials cause a significant decrease in dielectric constant due to evaporation of the electrode at high temperatures and interaction with the dielectric film. However, even with the above-mentioned high melting point noble metal electrode, electrode surface roughness occurs due to recrystallization when dielectric film is formed at 300° C. or higher. The dielectric film formed on such an electrode is not uniform in film thickness, and when a voltage is applied, a strong electric field is applied to a thinner part of the film, resulting in problems with insulation properties.

The electrode material widely used in current highly integrated circuits is polycrystalline silicon or a low-resistance silicon layer in which a portion of the silicon substrate itself is heavily doped with impurities. Hereinafter, these will be collectively referred to as silicon electrodes. Microfabrication technology for silicon electrodes has been established and is already widely used, so if a good high dielectric constant thin film can be produced on silicon electrodes, it will be possible to use them in capacitors for integrated circuits.

However, in the prior art, for example, IBM Journal of Research and Development (
IBM Journal of Research a
nd Development) November 1969 Issue 6
In the paper on 5rTi03 film published on pages 86-695, it is stated on pages 687-688 that when forming a thin film of a high dielectric constant material on silicon, approximately 100 layers equivalent to silicon dioxide (Si02) are required. It has been reported that it is formed at the interface. Since this interfacial layer has a low dielectric constant, the effective dielectric constant of the high dielectric constant thin film formed on silicon is greatly reduced, almost eliminating the advantage of using high dielectric constant materials. . Other examples of similar reports include the Journal of Vaccination, Science and Technology;
f Vacuum 5science and Tech
This can be seen in the description on page 316 of the paper on BaTiO3 published in Vol. 16, No. 2, pp. 315-318.

An object of the present invention is to use a thin film of a high dielectric constant material such as BaTiO3 and 5rTi03 to realize a thin film capacitor that has high capacitance density and excellent insulation properties and is applicable to silicon integrated circuits.

(Means for Solving the Problems) The present invention provides a thin film capacitor that is formed on a substrate and has a structure in which a lower electrode, a dielectric material, and an upper electrode are sequentially laminated. A thin film capacitor characterized by being made of one or more of osmium, rhodium, iridium, and their silicides or oxides, and a method for manufacturing the same.

(Example 1) Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 is a structural diagram of the thin film capacitor of Example 1, in which a silicon oxide film 2 is formed as an insulating layer on the surface of a silicon substrate 1, a lower electrode 3 is formed on the silicon oxide layer, and a dielectric layer is formed on the lower electrode. A BaTiO3 film 4 is formed, and an AI film 5 as an upper electrode is formed thereon.

First, an 1pm silicon oxide layer was formed on the surface of single crystal silicon by steam thermal oxidation. The atmosphere was controlled at a flow rate ratio of 1:1 of oxygen gas and hydrogen gas, and the temperature was 11:1.
Thermal oxidation was performed at 00°C. The lower electrode was fabricated with a film thickness of 0.5 pm by direct current magnetron sputtering. Using a dynamic or ReSi2 composition target, Ar gas atmosphere or mixed gas atmosphere of Ar and 02, 4X10-3
Torr, and the substrate temperature was 100°C.

A BaTiO3 film having a thickness of 0.5 pm was fabricated by high frequency magnetron sputtering using a powder target with a stoichiometric composition. In Ar-02 mixed gas, lXl0-
The film was formed by sputtering at 2 Torr and a substrate temperature of 600°C.

A 0.5 pm AI film was formed on the upper electrode by direct current sputtering. The effective area of this capacitor is 3 x 5mm2
It is.

Next, the difference in the characteristics of the BaTiO3 film when a Pd film, which is a high melting point noble metal, is used for the lower electrode and when the film age of this method is used will be described. Fig. 2(a) is a histogram of the dielectric breakdown strength of a BaTiO3 film using the lower electrode film of this method, and Fig. 2(b) is a histogram of the dielectric breakdown strength of a BaTiO3 film using a Pd film with a thickness of 0.5 pm. It is. The dielectric breakdown strength was defined as the electric field strength when a current of 1X10-'A/cm2 flows. The dielectric breakdown strength of this method is more than three times higher, and there is no variation in its distribution, indicating excellent insulation properties.

When a part of the BaTiO3 film was removed by etching and the surface roughness of the lower electrode was measured using a stylus type surface film difference meter, the average roughness h of the rhenium film and the Pd film was 50%.
A total of 380 people found that films made of rhenium had better surface flatness. Note that the surface roughness of the lower electrode before forming the BaTiO3 film is about 30. Therefore, the difference in insulation properties between the two is BaTiO3
This is thought to be caused by surface roughness of the lower electrode during the high-temperature process of film formation. In this case, the same effect was obtained even when the lower electrode was made of rhenium, rhenium oxide, rhenium silicide, or a laminated structure thereof.

Moreover, even when osmium, rhodium, iridium, and their silicides or oxides are used instead of rhenium, rhenium oxide, and rhenium silicide in this example, the dielectric breakdown strength of the BaTiO3 film formed thereon is still lower than that of the conventional one. More than 3 times larger than when using Pd film,
Excellent insulation properties were obtained. Table 1 shows the lower electrode materials and the materials formed thereon in Table 1 (Example 2). layer 7
is formed, a polycrystalline silicon film 8 is formed as a lower electrode on the silicon oxide layer, a film 9 made of rhenium or the like is formed thereon, a dielectric BaTiO3 film 10 is formed on these lower electrodes, and an upper electrode is formed on it. An AI film 11 is formed.

The polycrystalline silicon film is heated at 300° by plasma CVD method.
A film with a film thickness of 0.3 pm was prepared using C. Arsenic ions are applied to this polycrystalline silicon film at 2×101 at an accelerating voltage of 70 KV.
Ions were implanted in an amount of 6 cm-2, and further heated at 900 °C for 20
A sheet resistance of approximately 100 ΩC was achieved by heat treatment for a minute. The other films were formed in the same manner as in Example 1.

In this case, the polycrystalline silicon film is used to improve the adhesion between the silicon oxide of the insulating layer and the lower electrode, but even if a film of rhenium or the like is formed on the polycrystalline silicon film,
A thin film capacitor having excellent insulation properties as in Example 1 was obtained. Note that in the case of rhenium or rhenium oxide, a multilayer film containing metal silicide such as rhenium silicide and rhenium or polycrystalline silicon may be used instead of polycrystalline silicon.

(Example 3) FIG. 4 is a structural diagram of a thin film capacitor of Example 3. A low resistance layer 13 is formed by doping a portion of the surface of the single crystal silicon 12 with phosphorus at a high concentration, and a silicon oxide film 14 is formed thereon as an interlayer insulating film. Two contact poles are formed in a part of the silicon oxide film to draw out the lower electrode through the low resistance layer, one contact hole is filled with the lower electrode film 15, and the other contact hole is filled with the AI film 16. It is filled with Therefore, the AI film 16 becomes a terminal of the lower electrode. The lower electrode film fills the contact hole, and a portion of the lower electrode film may be formed on top of the silicon oxide film. A BaTiO3 film 17 is formed on the lower electrode film, and A118 is formed thereon as an upper electrode.

In this example, the lower electrode film is fabricated on single crystal silicon in order to draw out the lower electrode through the low resistance layer of single crystal silicon, but the insulation properties of the thin film capacitor are as excellent as in Example 1. I confirmed that there is.

Next, the difference in dielectric constant of the BaTiO3 film when a polycrystalline silicon film is used for the lower electrode and when the film of the present invention is used will be described. Polycrystalline silicon film is used in current silicon LSI
This is a material commonly used as an electrode film. Fifth
The figure shows the relationship between the dielectric constant and film thickness of a BaTiO3 film, and shows the results when the film of the present invention (a) is used and when a polycrystalline silicon film (b) is used.

When using the film of the present invention, the dielectric constant of the BaTiO3 film does not depend on its film thickness and is constant at about 240;
The dielectric constant of a BaTiO3 film when a polycrystalline silicon film is used depends on the film thickness, and the dielectric constant becomes smaller as the film thickness becomes thinner. This is considered to be because, as described in the prior art, a silicon oxide film with a low dielectric constant is formed at the interface between BaTiO3 and polycrystalline silicon, and the apparent dielectric constant of the BaTiO3 film is lowered.

Further, as in the second embodiment, the lower electrode may have a two-layer structure including a film made of rhenium or the like and polycrystalline silicon underneath. In this case, the polycrystalline silicon film has the effect of improving the adhesion between the rhenium film and the single crystal silicon and silicon oxide. Furthermore, a planarization technique for filling contact holes with a polycrystalline silicon film has been established, and there are great advantages to using it as part of the lower electrode.

As shown in this example, by using a film made of one or more of rhenium, osmium, rhodium, iridium, and their silicides or oxides for the lower electrode, a constant high dielectric constant can be achieved regardless of the thickness of the dielectric film. Thin film capacitors can be fabricated on silicon electrodes.

(Effects of the Invention) As explained above, the present invention uses iridium, which does not cause surface roughness during high-temperature processes, for the lower electrode of a thin film capacitor.
By using films of osmium, rhodium, iridium, their silicides or oxides, it is possible to provide a high dielectric constant thin film capacitor with excellent insulation properties.

In addition, unlike conventional silicon electrodes, there is no need to form a silicon oxide layer with a low dielectric constant at the interface with the dielectric, so thin film capacitors with a constant high dielectric constant regardless of the thickness of the dielectric film can be created. Can be fabricated on silicon.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional side view of a thin film capacitor showing an embodiment of the present invention, Figs. 2(a) and (b) are histograms of dielectric breakdown strength, and Figs. 3 and 4 are thin film capacitors showing an embodiment. FIG. 5 is a diagram showing the relationship between the dielectric constant and the film thickness of the BaTiO3 film. 1.6.12 is a single crystal silicon substrate, 2.7.14 is silicon oxide, 3.9.15 is a lower electrode, 4.10.17
is BaTiO3, 5, 11, 16, and 18 are AI, 8 is polycrystalline silicon, and 13 is a low resistance layer of single crystal silicon.

Claims (4)

[Claims] 1. In a thin film capacitor formed on a substrate and having a structure in which a lower electrode, a dielectric material, and an upper electrode are sequentially laminated, the lower electrode on which the dielectric material is directly formed is one or more selected from rhenium, rhenium oxide, and rhenium silicide. A thin film capacitor characterized by being made of a material. 2. In a thin film capacitor formed on a substrate and having a structure in which a lower electrode, a dielectric material, and an upper electrode are sequentially laminated, the lower electrode on which the dielectric material is directly formed is one or more selected from osmium, osmium oxide, and osmium silicide. A thin film capacitor characterized by being made of a material. 3. In a thin film capacitor that is formed on a substrate and has a structure in which a lower electrode, a dielectric material, and an upper electrode are sequentially laminated, the lower electrode on which the dielectric material is directly deposited is selected from rhodium, rhodium oxide, and rhodium silicide. A thin film capacitor characterized by being made of one or more materials. 4. In a thin film capacitor that is formed on a substrate and has a structure in which a lower electrode, a dielectric material, and an upper electrode are sequentially laminated, the lower electrode on which the dielectric material is directly deposited is selected from iridium, iridium oxide, and iridium silicide. A thin film capacitor characterized by being made of one or more materials.